Field
The invention relates to a communications device, a communications network and a communications method.
Description of Related Art
An encrypted exchange of data via a common medium such as the Internet without the need to grant unauthorised access to the data transmitted is of great importance (protection of confidentiality). Symmetrical encryption methods such as AES (Advanced Encryption Standard; German: fortschrittlicher Verschüsselungsstandard) are conventionally used for applications which require a high level of security. With symmetrical encryption methods, the encryption is implemented by means of a code, which is known only to the transmitter and the receiver, and by means of an initialisation vector, which is transmitted from the transmitter to the receiver together with encrypted data.
A device and a method in which a datastream is subdivided into individual blocks are known from DE 10 2008 013 785 A1, whereas the individual blocks are encrypted and whereas a common checksum is calculated over the individual, encrypted data blocks. A method known as the “Galois Counter Mode” (German: Galois Zählermodus) is used for this purpose.
The disadvantage with DE 10 2008 013 785 A1 is that the initialisation vectors used in that context are issued randomly. That is, it is possible for transmissions which are encrypted by means of an identical code also randomly to provide an identical initialisation vector. In particular, with transmissions at a fast data rate, in which a new random initialisation vector is formed frequently, it can occur that two packets with an identical code and an identical initialisation vector occur. Accordingly, it is possible to draw conclusions with regard to the information content of the unencrypted data without needing to implement a complete decryption. In particular, this can occur in practice in the case of large-scale communications networks which use a uniform code.